Electron transfer reaction in the chromium(VI)-manganese(II) system in the presence of ethylenediaminetetraacetic acid (EDTA)

Upon addition of Cr-VI to a solution of ethylenediaminetetraacetic acid (EDTA) and Mn-II, a transient species appears which has an absorption maximum at 500 run. Kinetic studies of the outer-sphere oxidation of the Mn-II- EDTA complex with the Cr-VI-EDTA complex have been investigated by visible spectrophotometry at 25degreesC. The formation of a transient species has been characterized spectrophotometrically and the encounter complex formation constants have been determined (K-OS = 1.75 x 10(2) and 1.66 x 10(3) mol(-2) dm(6) for [EDTA] and [Mn-II] variations, respectively). The effect of total [EDTA], [Mn-II], [Cr-VI and [HClO4] on the rate of the reaction was determined. On addition of HClO4, there is a decrease in the rate constants. The reaction product is the Cr-III-EDTA complex with lambda(max) = 400 and 550 nm. On the basis of the various observations and product characterization a most plausible outer-sphere mechanism has been envisaged.